The immediate goal of the candidate, Keith G. Nelson, DVM, is to complete a mentored training program in research of immunopathogenesis of Leishmania infection, which will culminate in both the PhD degree and continued postdoctoral study. Dr. Nelson's long-term goal is to become a principal investigator conducting research on the immune response to, pathogenesis and prevention of leishmaniasis and other vector-borne parasitic pathogens. The research-training program will be centered on the laboratory of Dr. Richard G. Titus, in the immunoparasitology Research Group at Colorado State University. The research environment has a strong history of extramural funding and biomedical scientist training. The candidate's training plan consists of laboratory and didactic instruction in contemporary molecular and immunological techniques and research methods applied to an animal model of leishmaniasis. The proposed research utilizes an established murine model of Leishmania infection to investigate the early stages of the immune response to Leishmania major(Lm) and subsequent Type 1 T cell vs. Type 2 T cell (Th1/Th2) differentiation, with a focus on the macrophage receptors and parasite surface antigens involved in host recognition and response. Three specific aims will be addressed: 1) to identify the macrophage complement and non-complement receptors involved in recognition, phagocytosis, and response to Lm, as well as characterizing changes in the Th1/Th2 response secondary to entry via specific macrophage receptors; 2) to characterize the role of toll-like receptors TLRs) in transducing host response to Lm infection, identifying relevant receptors and determining the effect on Th1/Th2 bias; 3) to determine the effect of major parasite surface molecules lipophosphoglycan (LPG) and gp63 on host recognition, phagocytosis and Th1/Th2 response to Lm. All of these will be addressed using in vivo infection of relevant knockout mice with LPG or gp63 deficient parasites, as well as with in vitro macrophage culture, receptor blocking, infection and co-cultivation with naive Th cells to assess functional priming. Cytokine profiles will be assessed via ELISA and RTPCR to determine Th1/Th2-associated bias and TLR mRNA will be assessed via RT-PCR. The results of these studies will provide new insights into the interactions between the primary phagocytic ceils of the innate immune response and the protozoan parasite Leishmania major. We will also gain insight into the effect of the innate immune response and pathogen recognition pathway on the establishment of Th1/Th2 responses in adaptive immunity. This information may prove to be important in the development of effective treatment, control and preventative measures in leishmaniasis, as well as furthering our knowledge of the interactions between the innate and adaptive arms of the immune system.